<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>

    .yeye{
        width:400px;
        height:400px;
        background:olive;
        padding:30px;
    }

    .baba{
        width:300px;
        height:300px;
        background-color:black;
        position:relative;
    }

    .a,.b,.c{
        width:200px;
        height:60px;
    }

    .a{
        background-color:palevioletred;
    }

    .b{
        background-color:darkcyan;
        position:absolute; /*绝对定位*/
        top:30px;
        left:50px;
    }

    .c{
        background:chocolate;
    }
</style>
<body>
    
    <div class="yeye">
        <div class="baba">
            <div class="a"></div>
            <div class="b"></div>
            <div class="c"></div>
        </div>
    </div>
</body>
</html>